Gear shifting control method for hydraulic automatic transmission during interruption of communication with engine

The gear shifting control method comprises the steps that 1, a transmission controller detects a CAN bus communication message in real time, and when the communication is interrupted or a message signal is lost, the step 2 is executed; 2, the transmission controller obtains internal configuration parameters and internal default parameters of the controller; 3, the transmission controller obtains the engine rotating speed, the transmission input shaft rotating speed and the transmission output shaft rotating speed in real time; 4, the target gear of the transmission is calculated, and meanwhile the lowest protection gear and the highest protection gear which are allowed to operate by the transmission are calculated; step 5, outputting a final target gear; 6, locking and separation control over the hydraulic torque converter is conducted; and 7, gear shifting control is carried out. According to the invention, the problem of safe driving under the condition that the CAN bus communication between the transmissio